And yes, Warsaw, I agree that very few people would answer the phone "Yes, this is she," but what if it were:
Sara: Hello
Natasha: is it Sara speaking?
Sara: yes, it is Sara.
Nat: Is it really she?
Sara: yes it is really she.

Thanks guys! For the illumination.
I think it depends on the situation you are talking about. for instance, in academic writing or in tests where the connection to the reality is not considered it should always be "follow the sequence" way; while in real-life situations--like in a conversation--you should follow the logical sequence, because , otherwise, the statement would become awkward. And, if you are writing a letter to the principal (of my example), where you are not sure if the good library still exists or not (you might get a response: "We closed the library to cut annual expenses") it is better to follow the sequence of tenses.

A colon is used for various reasons in BE or NAmE:
to introduce a list; to introduce a quotation; to give an explanation (cause, etc) of the aforesaid; to tell rules and regulations; to tell reasons; and after a short introductory phrase to introduce the main sentence.
NOW,
Capitalize if:
* list has proper nouns (All except Peter were there: Samantha, Ted, Natasha...),
* if the clause after the colon is a complete standalone sentence meant to explain the aforesaid (Napoleon Bonaparte had to suffer the consequences of delay made by one of his generals: Time and tide wait for none.),
* if the introductory phrase introduces a formal quote (This was what Sir Winston Churchill had to say about dictatorship: "Dictators ride to and fro upon tigers which they dare not dismount. And the tigers are getting hungry."),
* if the explanatory statement after the colon consists of more than one sentence, begin, the first sentence with a capital (The drop in enrolment this year may be ascribed to many concomitant causes: First, the last year's incident of the on-campus rape. Second...)
* If the introductory phrase is very short and the main sentence is what follows the colon (Understand: Some adjectives may only be used as predicative adjectives and never as attributive adjectives.)
* If the clause before the colon is meant just to introduce the clause after the colon (Let us repeat that again: Some adjectives may only be used as predicative adjectives and never as attributive adjectives.)
* all the tenants must take care of the first clause of the contract: No tenant is allowed to sublet his/her apartment in any case.)

I hope that helps